Those skilled in the art of marine propulsion systems are aware of many different types of transmissions that are used to shift marine drives between forward, neutral and reverse positions. In single propeller systems, it is common to locate facing forward and reverse bevel gears in the propeller housing at a lower right angle connection between the vertical drive shaft and the propeller shaft with a clutch mechanism in the propeller housing shifting between neutral, forward and reverse positions. In dual counter-rotating propeller systems, however, the two facing bevel gears in the propeller housing are each fixed to a respective propeller and shifting between forward, neutral, and reverse positions must take place upstream in the torque path. In dual propeller stern drive arrangements, the forward and reverse functions are often accomplished at the upper right angle connection in the stern drive housing between the engine output shaft and the top end of the vertical drive shaft. This means of shifting between forward, neutral and reverse is not available, however, when one employs dual-counter rotating propellers in an outboard motor.
The present disclosure provides an in-line forward, neutral and reverse transmission that can be located on the vertical drive shaft upstream of the lower right angle gear connection in the propeller housing of a marine drive. Such an in-line transmission has the potential to simplify the construction of single propeller and dual propeller outboard motors as well as other types of marine drives. It is desirable that such an in-line transmission be efficient and robust, and have relatively low inertia and weight. Many of the options for locating the forward, neutral and reverse function upstream of the propeller housing in outboard motors rely on complex planetary transmissions or wet clutches that are relatively inefficient, heavy, bulky and expensive. Lay shaft or counter-rotating shaft arrangements with gearing or chain drives are viable but have been found to be too large and complex for some applications.